1. Field of the Invention
The invention relates to a bicycle derailleur. More specifically, this invention relates to a front derailleur for a bicycle adapted to be installed on a frame of the bicycle, configured and arranged to be connected to a gear shift to guide a chain into one of a plurality of gear shifting positions in accordance with movement of the gear shifting cable.
2. Background Information
Japanese Laid-Open Patent Publication No. H08-169382 discloses a conventional a gear shifting device of a bicycle, a front derailleur, which is configured and arranged to guide a chain into one of a plurality of front sprockets. The conventional front derailleur is provided with a base member installed on a frame of the bicycle, internal and outer links arranged in parallel and are mutually freely rotatably connected on one ends to the base member, and a chain guide connected to the other ends of the internal and outer links to guide the chain. In the conventional front derailleur, a twist coil spring is provided for applying a biasing force to the chain guide in a direction toward the frame. The twist coil spring is disposed around a connecting shaft between the base member and the external or inner link. The internal or outer link is configured and arranged to be attached to a shift cable.
In the conventional front derailleur as disclosed in the above mentioned reference, when the shift cable is pulled by the gear shifting operation, the internal and outer links swings so that the chain guide moves in a direction away from the frame to up-shift the gear. Then, when the shift cable is returned by the gear shifting operation, the biasing force by the twist coil spring moves the chain guide in a direction toward the frame to down-shift the gear.
In the conventional front derailleur, as the biasing force is applied on the chain guide in the direction toward the frame via the internal or outer link due to the twist coil spring, the spring force becomes greater in proportion to the rotation amount of the internal or outer link (e.g., a twisting amount of the twist coil spring). Thus, the torque acting on the internal or outer link becomes greater in proportion to the rotation amount of the internal or outer link as well. Therefore, when the gear is up-shifted into the highest speed, the maximum force acts upon the shift cable and the greatest operational force is necessary for up-shifting operation. As a result, the shifting operation becomes difficult because a greater force is required for the gear shift operation when the gear shift operation is performed manually by a gear shifting member. Also, when the gear shift operation is performed by using a motor, a large motor is required to generate a required torque. Thus, life of the power source is influenced and it is difficult to design the bicycle to be lightweight.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved front derailleur. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.